Refrigeration system utilizing natural circulation of heat to carry out defrosting thereof

ABSTRACT

A refrigeration system utilizing natural circulation of heat to carry out defrosting thereof provides a refrigeration cycle path and a defrost cycle path, and is characterized by a heat energy storage device located at an output of a compressor that is common for the two cycle paths. High-temperature high-pressure overheated refrigerant output by the compressor passes through the heat energy storage device and releases part of heat energy thereto for storage. When the refrigeration system is switched from the refrigeration cycle path to the defrost cycle path, the compressor is turned off and three-way valves upstream an evaporator are opened, a pressure difference between the heat energy storage device and the evaporator drives the hot refrigerant to directly flow through the three-way valves into a coil of the evaporator to melt frost on the coil from inner to outer side while the refrigerant keeps circulating along the defrost cycle path.

FIELD OF THE INVENTION

The present invention relates to a refrigeration system, and more particularly to a refrigeration system that includes a heat energy storage device provided at an outlet of a compressor, so that high-temperature high-pressure overheated refrigerant output from the compressor passes through the heat energy storage and releases part of heat energy thereto, and a pressure difference between the refrigerant in the heat energy storage device and the refrigerant in an evaporator drives the refrigerant to circulate through the evaporator in a defrost cycle of the refrigeration system to achieve the purpose of defrosting the evaporator.

BACKGROUND OF THE INVENTION

Please refer to FIG. 1. A conventional refrigeration system includes a compressor 1, a condenser 3, an expansion valve 4, an evaporator 5, a liquid collector 6, and other related parts. The refrigeration system is widely applied to many devices in people's daily life, such as refrigerated showcases and refrigerators or freezers in supermarkets and hypermarkets, as well as refrigerated warehouses, refrigerated storerooms and other refrigeration apparatus for general refrigeration purposes and logistics of refrigerated or frozen products. The refrigeration system for general refrigerating devices is based on a refrigerant vapor-compression refrigeration cycle system. In the refrigeration cycle system, the evaporator 5 is a refrigeration heat exchanger. Air is cooled by the evaporator 5, and moisture in the air condenses to form frost on outer surfaces of the heat exchanger. The frost accumulated on the outer surfaces of the heat exchanger becomes thicker and thicker when the refrigeration cycle continues. The accumulated frost has adverse influence on the operation of the refrigeration cycle system and must be timely removed. The forming of the frost is inevitable. However, the accumulated frost would generally cause the following problems:

-   -   (1) Resulting in thermal impedance: The frost forms a resistance         to heat transfer and would cause insufficient heat exchange and         accordingly, lowered refrigeration capacity;     -   (2) Resulting in deteriorated refrigeration cycle efficiency:         Due to the largely lowered refrigeration capacity, the         compressor consumes more power to result in lowered         refrigeration efficiency; and     -   (3) Causing rising temperature in the refrigerated space: Since         the frost forms a resistance to heat transfer, air passing the         evaporator could not be effectively cooled and the temperature         in the refrigerated space gradually raises to adverse influence         the quality of refrigerated products.

A common solution to the accumulated frost is to defrost the evaporator. Defrosting requires additional power consumption. Heat-driven defrosting is the most common way for removing frost. And, the heat-driven defrosting can be achieved by several different heating means, including external electrical heating, internal electrical heating, compressor-produced hot gas, and hot water.

These heating means for defrosting respectively have the following disadvantages:

-   -   (1) External electrical heating: When using this heating means,         the compressor is turned off and the heat for defrosting is         electrically generated and thereby requires additional power         consumption to obtain it. Since the frost is heated from outer         to inner side, longer time and more power consumption are         required to fully melt the thick frost and separate it from the         evaporator. Further, since the heat works in the refrigerated         space during the defrosting process, the temperature in the         refrigerated space also rises to adversely affect the quality of         the refrigerated products.     -   (2) Internal electrical heating: When using this heating means,         like the external electrical heating, the compressor is also         turned off. However, the frost is heated from inner to outer         side, so that the frost at the inner side melts to separate from         the evaporator first and it is not necessary to wait for full         melting of the frost at the outer side. Therefore, even if the         internal electrical heating also consumes additional electric         power and also results in rising temperature in the refrigerated         space, it requires shorter time to achieve the purpose of         defrosting compared to the external electrical heating.     -   (3) Compressor-produced hot gas: When using this means, hot gas         output by the compressor is directly guided by a four-way valve         into the coil of the evaporator to melt the accumulated frost on         the coil from inner to outer side. Like the internal electrical         heating, this means requires shorter time to defrost the         evaporator. However, with this means, the compressor keeps         operating during the defrosting process to consume additional         power. Further, there would be a temperature difference more         than 100° C. when the refrigerant changes from the vaporization         temperature to the condensation temperature. Such a big         temperature difference tends to cause thermal shock, resulting         in a damaged coil of the evaporator due to an instantaneous         temperature change thereof.     -   (4) Hot water: When using this means, hot water is sprayed on         the accumulated frost to melt the same from outer to inner side         thereof, and refrigerated products must be removed from the         refrigerated space before spraying the hot water. This heating         means has the disadvantages of requiring additional heat energy         for the hot water supply, requiring longer time to fully melt         the frost from outer to inner side, and troublesomely requiring         extra efforts to remove the refrigerated products from the         refrigerated space and properly keep them at original         refrigeration temperature to avoid adverse influence on the         quality of the refrigerated products.

In view of the disadvantages in the above-mentioned defrosting means, as well as the inevitable forming of frost and the necessity of removing the accumulated frost of a considerable thickness, it is tried by the inventor to work out an effective way of defrosting that does not consume or require additional energy and overcomes the inconveniences and drawbacks in the conventional defrosting ways, so as to solve the defrosting problems that have confused consumers over a long time and to achieve the purpose of energy saving and carbon reduction.

SUMMARY OF THE INVENTION

To achieve the above object of providing an effective way of defrosting that does not consume or require additional energy and overcomes the inconveniences and drawbacks in the conventional defrosting ways, the technical means adopted by the present invention include:

-   -   (1) Utilizing recycled waste heat from the refrigeration system         itself to defrost the evaporator without the need of consuming         additional electrical energy or other types of energy;     -   (2) Omitting the four-way valve to thereby simplify the         refrigeration system and reduce the manufacturing cost thereof;     -   (3) Melting the accumulated frost from inner to outer side to         more quickly achieve the purpose of defrosting the evaporator;     -   (4) Using natural circulation of heat to carry out defrosting         without the need of using pumps or other electrical devices or         the need of consuming additional energy supplied by other         electric devices;     -   (5) Turning off the compressor and the fans or electrical pumps         for the condenser and the evaporator in the process of         defrosting, so as to reduce the power consumed by the         refrigeration system during defrosting thereof;     -   (6) Turning off the compressor for the refrigerant output         therefrom to have gradually risen temperature when the         defrosting is initiated, so as to protect the evaporator against         damage by the thermal shock effect on the evaporator due to         instantaneous big temperature difference; and     -   (7) Using the conventional refrigeration system as much as         possible by integrating a defrost cycle path into the originally         existed refrigeration cycle path to reduce the cost for setting         up an additional individual defrosting system.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein

FIG. 1 is a diagram of a conventional refrigeration system;

FIG. 2 is a diagram of a refrigeration system according to a first embodiment of the present invention; and

FIG. 3 is a diagram of a refrigeration system diagram according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with some preferred embodiments thereof and with reference to the accompanying drawings. For the purpose of easy to understand, elements that are the same in the preferred embodiments are denoted by the same reference numerals.

Please refer to FIGS. 2 and 3 that are diagrams of refrigeration systems according to a first and a second embodiment of the present invention, respectively. As shown, the refrigeration system of the present invention, either in the first or the second embodiment, includes a refrigeration cycle path indicated by the dark lines “a” and a defrost cycle path indicated by the light-colored lines “b”. Compared to the conventional refrigeration system shown in FIG. 1, the refrigeration system according to the present invention further includes at least one heat energy storage device 2, which can be installed in series or in parallel to an outlet 11 of the compressor 1. A refrigerant is compressed in the compressor 1 and output as a high-temperature, high-pressure and overheated refrigerant, which passes through the heat energy storage device 2 to release part of heat energy therein and the released heat energy is stored in the heat energy storing device 2.

The heat energy storage device 2 is formed of a heat energy storage material having a relatively high specific heat. One type of heat energy storage material is sensible heat storage material, which stores and releases heat energy through temperature change. Some common sensible heat energy storage materials include rocks and high-temperature concrete. These materials have relatively high specific heat and are low in cost. Recently, since molten salt has high specific heat and can serve as a heat transfer medium, potassium nitrate and sodium nitrate are frequently combined with salts to serve as sensible heat energy storage materials. Another type of heat energy storage material is latent heat energy storage material, which combines the characteristics of sensible heat with those of phase-change latent heat and stores heat by absorbing heat and releasing heat during solid/liquid/gas phase changes under a constant temperature condition. The phase-change latent heat energy storage material has a heat storage density much higher than that of the sensible heat energy storage material, and therefore provides more advantages in terms of heat energy storage, storage volume and energy storage density. Water is also frequently selected for use as a heat energy storage medium due to its easy availability and low cost.

The heat energy storage device 2 must coordinately work with the condenser 3. The cooling of the condenser 3 must be controlled in the process of heat energy storage, so that the heat energy stored in the heat energy storage device 2 and the stable cooling of the condenser 3 together ensure stable operation of the compressor 1 and stable refrigeration performance of the refrigeration system. For example, in the refrigeration cycle path, after releasing part of its heat energy to the heat energy storage device 2, the high-temperature high-pressure refrigerant directly flows to the condenser 3 and releases heat energy again to go into a high-pressure low-temperature saturated or undercooled state. The refrigerant then passes through the expansion valve 4, at where the refrigerant is reduced in pressure and expands in volume to go into a low-pressure low-temperature state. The refrigerant enters the evaporator 5 in the low-pressure low-temperature state and absorbs heat from air in the refrigerated space to thereby vaporize into a low-pressure saturated gaseous or overheated state. Then, the vaporized refrigerant enters the liquid collector 6, at where vapor and liquid are separated, and the low-pressure gaseous refrigerant is sucked in by the compressor 1 to complete one refrigeration cycle.

Moisture in the air in the refrigerated space is condensed to form frost on outer surfaces of the coil and fins of the evaporator 5. The frost accumulates when the refrigeration cycle continues. Since the buildup frost would result in lowered refrigeration efficiency and freezing performance, it is necessary to defrost the evaporator 5. Please refer to FIG. 2 or 3 for the defrost cycle path according to the present invention as indicated by the light-colored lines “b”. When the defrost cycle is initiated, the compressor 1 is turned off, heat transmission devices, such as fans or pumps, for the condenser 3 and the evaporator 5 are also turned off. The heat energy storage device 2 at this point has already stored a certain amount of heat energy, and the refrigerant in the heat energy storage device 2 absorbs heat and vaporizes to produce pressure therein. The pressure produced by the vaporized refrigerant in the heat energy storage device 2 is higher than the pressure produced by the refrigerant at the low-pressure end, i.e. higher than the pressure at the evaporator 5, the liquid collector 6 and the inlet of the compressor 1, so that there is a pressure difference between the heat energy storage device 2 and the evaporator 5, and the pressure difference is large enough to drive the refrigerant to flow. When two three-way valves 7, 8 located upstream the condenser 3 and the evaporator 5, respectively, are opened, the refrigerant will flow and circulate along the path indicated by the light-colored lines without passing through the condenser 3 to thereby have lower pressure lose. Further, in the defrost cycle path, the refrigerant also does not pass through the expansion valve 4 that provides high resistance to the refrigerant flow. In brief, the refrigerant directly flows from the heat energy storage device 2 into the coil of the evaporator 5 via the three-way valves 7, 8 located upstream the evaporator 5. As a result, the coil and fins of the evaporator 5 are heated by the refrigerant, and the frost externally accumulated on the coil and fins gradually melts from inner to outer side. Due to the pressure difference between the heat energy storage device 2 and the evaporator 5 created by the heat energy stored in the heat energy storage device 2, the refrigerant is driven to circulate along the defrost cycle path to achieve the purpose of defrosting the coil and fins of the evaporator 5.

After the defrost cycle has been continued for a properly preset time period, the fan for the evaporator 5 is turned on. At this point, the accumulated frost in direct contact with the coil and the fins of the evaporator 5 has already melted and is no longer attached to the outer surfaces of the coil and fins even if the outer portion of the accumulated frost has not yet melted. Therefore, the frost quickly separates from the surfaces of the coil and the fins after the fan of the evaporator 5 is tuned on. In case that the heat energy storage device 2 has insufficient heat storage capacity in design, a heating device, such as an electric heater (not shown), can be additionally provided on the heat energy storage device 2 and be timely actuated to cooperatively work with the stored heat for driving the refrigerant to circulate along the defrost cycle path.

The present invention has been described with some preferred embodiments thereof and it is understood that many changes and modifications in the described embodiments, such as connecting one single heat energy storage device to multiple compressors in one refrigeration system, can be carried out according to different requirements in actual use environment without departing from the scope and the spirit of the invention that is intended to be limited only by the appended claims. 

What is claimed is:
 1. A refrigeration system utilizing natural circulation of heat to carry out defrosting thereof, comprising a compressor, a heat energy storage device, a condenser, an expansion valve, an evaporator internally having a coil and a plurality of fins, a liquid collector and a plurality of three-way valves to provide a refrigeration cycle path and a defrost cycle path; the compressor being common for the refrigeration cycle path and the defrost cycle path, and the heat energy storage device being installed at an outlet of the compressor, so that a refrigerant compressed by the compressor and output as a high-temperature, high-pressure overheated refrigerant passes through the heat energy storage device and releases part of heat energy, and the released heat energy is stored in the heat energy storage device; whereby when the refrigeration system is switched from the refrigeration cycle path to the defrost cycle path for defrosting the evaporator, the compressor is turned off and the three-way valves located upstream the condenser and the evaporator are opened, a pressure difference between the high-temperature and high-pressure refrigerant in the heat energy storage and the low-temperature and low-pressure refrigerant in the evaporator drives the refrigerant to directly flow through the three-way valves located in the defrost cycle path and upstream the evaporator into the coil of the evaporator without passing through the condenser and the expansion valve; and when the hot refrigerant flows through the coil, frost externally accumulated on the coil and the fins of the evaporator is melted from inner to outer side; and, due to the pressure difference between the heat energy storage device and the evaporator, the refrigerant keeps circulating along the defrost cycle path to defrost the evaporator.
 2. The refrigeration system utilizing natural circulation of heat to carry out defrosting thereof as claimed in claim 1, wherein the heat energy storage device is formed of a heat energy storage material having a relatively high specific heat.
 3. The refrigeration system utilizing natural circulation of heat to carry out defrosting thereof as claimed in claim 1, further comprising a heat device provided on the heat energy storage device. 